Among denitration catalysts for use in the removal of nitrogen oxides from an exhaust gas are those which comprise a glass fiber or ceramic fiber as a carrier for the purpose of improving water resistance or electrical insulating properties. In particular, fibers made of glass called E-glass are known to be excellent in water resistance or electrical insulating properties.
However, E-glass fiber contains B.sub.2 O.sub.3 and thus is disadvantageous in case where the exhaust gas contains sulfur oxides (SO.sub.3) since B.sub.2 O.sub.3 reacts with sulfur oxides to produce metal salts which are then eluted from the fiber matrix to deteriorate the fiber. Further, ceramic fiber is similarly disadvantageous. For example, alumina-containing fiber is liable to the reaction of Al.sub.2 O.sub.3 with sulfur oxides that causes the deterioration of the fiber. Moreover, since Al.sub.2 O.sub.3 exists in glass as a main component with SiO.sub.2, a carrier made of E-glass fiber is liable to the reaction of both B.sub.2 O.sub.3 and Al.sub.2 O.sub.3 with sulfur oxides that causes further deterioration of the carrier.